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Hypersomnolence disorder (HD) is characterized by excessive sleep, which is a common sequela following stroke, infection, or tumorigenesis. HD is traditionally thought to be associated with lesions of wake-promoting nuclei. However, lesions of a single wake-promoting nucleus, or even two simultaneously, did not exert serious HD. Therefore, the specific nucleus and neural circuitry for HD remain unknown. Here, we observed that the paraventricular nucleus of the hypothalamus (PVH) exhibited higher c-fos expression during the active period (23:00) than during the inactive period (11:00) in mice. Therefore, we speculated that the PVH, in which most neurons are glutamatergic, may represent one of the key arousal-controlling centers. By using vesicular glutamate transporter 2 (vglut2Cre) mice together with fiber photometry, multichannel electrophysiological recordings, and genetic approaches, we found that PVHvglut2 neurons were most active during wakefulness. Chemogenetic activation of PVHvglut2 neurons induced wakefulness for 9 hr, and photostimulation of PVHvglut2→parabrachial complex/ventral lateral septum circuits immediately drove transitions from sleep to wakefulness. Moreover, lesioning or chemogenetic inhibition of PVHvglut2 neurons dramatically decreased wakefulness. These results indicate that the PVH is critical for arousal promotion and maintenance.